The present invention relates to a data recording and reproducing apparatus for use in reproducing data at high speed.
Known recording and reproducing apparatus are able to record and reproduce data by directly accessing an arbitrary recording and reproducing position unlike hard disk apparatus and magneto-optical disk apparatus which record and reproduce data in the order of time series.
Data handled by the hard disk apparatus and the magneto-optical disk apparatus are formed of 512-byte blocks and collected in the unit of sectors. Upon recording, it is customary that data are recorded on a recording medium at the unit of clusters each of which is formed of 8 sectors, for example.
When data of a certain unit amount is recorded on a recording medium as one cluster, if consecutive data, such as an audio signal or the like from a time standpoint, is recorded on the recording medium, then it is frequently observed that a plurality of consecutive data from a time standpoint are recorded on the recording medium at physically distant positions.
In this case, when data that is recorded at a plurality of fundamental units is reproduced, it is unavoidable that a reproducing head is physically moved at connected portions of the fundamental units. Thus, a useless time occurs. This disadvantage will be described below with reference to FIG. 1 of the accompanying drawings.
In FIG. 1, Rb [bps] assumes a read speed of a reproducing head, A [sec] assumes a moving speed of the reproducing head, S [bit] assumes fundamental unit data amount, Fs [Hz] assumes a data sampling frequency and Qi [bit] assumes data quantization bit rate.
At that time, a data read time with which the reproducing head reads fundamental unit data 1 to 4 recorded on a recording medium 80 at its arbitrary positions is given by S/Rb [sec]. On the other hand, a fundamental unit reproducing time which a recording and reproducing apparatus outputs at one time normal speed is given by S/(Ql.multidot.Fs)[sec]. Unless the reproducing head is moved to the next fundamental unit and reads data during the recording and reproducing apparatus reproduces data of one fundamental unit, then an output of the recording and reproducing apparatus becomes discontinuous. Thus, we have: (S/Rb)+A.ltoreq.S/(Ql.multidot.Fs)
When the recording and reproducing apparatus reproduces data at twice normal speed, a fundamental unit reproducing time is given by S/(Q1.multidot.Fs.multidot.2) [sec] and the condition equation is given by (S/Rb)+A.ltoreq.S (Q1.multidot.Fs.multidot.2) [sec]. The read speed Rb of the reproducing head is constant for the same medium and the moving time A of the reproducing head also is constant. Thus, if the data sampling frequency Fs and the data quantization bit rate Q1 are made constant, then when the recording and reproducing apparatus reproduces data at twice normal speed, it is necessary to increase the fundamental unit data amount S as compared with the case that the recording and reproducing apparatus reproduces data at one time normal speed. As the fundamental unit data amount is increased, a standby time required when data is accessed is increased.
Further, in the recording and reproducing apparatus, if the reproducing speed is selected to be one time normal speed, e.g., twice normal speed, then data has to be read within a half time of a time required when data is reproduced at one time normal speed. In order to read data within the half time, data of the increased fundamental unit data amount S has to be processed. There is then the disadvantage that it is difficult to design such recording and reproducing apparatus in actual practice.